The technology described herein relates generally to methods for making hollow metal objects, and more particularly to such objects for use as airfoils for gas turbine engines.
Many gas turbine engine assemblies include hollow metal objects, such as airfoils in the form of fan blades, and/or non-rotating stationary airfoils, such as guide vanes. Hollow areas within the object may be utilized to reduce weight and/or impart other desirable structural properties.
Hollow metal structures with good properties and dimensional control are often difficult to manufacture and may be expensive due to processing complexity and low yield with conventional processes.
Hollow metal structures have been created by several methods. Casting is affordable, but thin wall sections can be difficult to control and material properties can be poor. Fabrication can be done multiple ways. The component parts can be cut and formed from sheet metal, cast, milled and/or ‘Super Plastic Formed’. The bonding may be by fusion welding, solid state welding, diffusion bonding, activated diffusion bonding, brazing, bolting, or adhesive bonding. Welding creates local heat affected zones which may require subsequent heat treatment. Brazing and activated diffusion bonds may have local inferior property regions due to local alloying. Adhesive bonds may lack sufficient strength. Prolonged processing at elevated temperature can degrade material properties such as fatigue and ductility.
There remains a need for improved manufacturing methods for making hollow metal objects which are cost effective and yield structures with good physical properties and dimensional control.